1. Field of the Invention
The present invention relates to an image forming apparatus using electrophotography, and more particularly, to an image forming apparatus in which the development and cleaning of an image carrier are simultaneously effected by a developing unit.
2. Description of the Related Art
Modern image forming apparatuses of this type are disclosed in, for example, U.S. Pat. Nos. 4,664,504 and 4,834,424. In these apparatuses, a developing process is executed such that a developing unit is used to cause a toner (coloring powder) as a developing agent to adhere to an electrostatic latent image on an image carrier, such as a photoconductor, thereby forming a toner image thereon. Thereafter, the toner image on the image carrier is transferred to a recording medium such as plain paper. After the transfer, residual or untransferred toner particles remaining on the image carrier are removed therefrom by means of the developing unit in the next image forming cycle.
Since the image carrier is thus cleaned by means of the developing unit, in these conventional image forming apparatuses, no exclusive-use cleaner is required for the cleaning, so that the image carrier can be miniaturized. Thus, the whole apparatus can be reduced in size and cost, and improved in maintenance efficiency. Accordingly, there is an urgent need for the apparatus of this type.
In these conventional apparatuses, however, if toner particles remain on the image carrier without being transferred to the recording medium during a transfer process in the preceding image forming cycle, the image carrier is charged and exposed through the untransferred toner particles in the subsequent cycle. As a result, the image carrier suffers uneven charging or exposure, so that undesired images may be produced.